The present invention relates to a method for manufacturing a light emitting device.
Recently, the semiconductor light emitting device using gallium nitride and related compound semiconductors (hereinafter called III-V nitride semiconductors) has attracted a lot of attention. Accordingly, the device structure suitable for the III-V nitride semiconductor has been studied.
Here, III-V nitride semiconductor is defined as the semiconductor of the compound of GaN of III group atom with N of V group atom, the compound of Ga of III group atom with another III group atom such as Al, In and others which is substituted for a part of Ga, and the compound of N of V group atom with another V group atom such as P, As and others which is substituted for a part of N.
Heretofore, various types of element structure have been proposed in order to improve the characteristics of the semiconductor light emitting device. As a method for improving a basic characteristic such as the threshold of oscillation, there is a method for providing structure to restrict the path for electric current.
As one of the methods to restrict the electric current path, there is a method of removing an area around the path in a p-type layer of the surface of the semiconductor by wet etching or dry etching.
However, the method has following problems.
The method of wet etching can not be used, because an etching solution suitable for the semiconductor of the GaN related compound has not been discovered.
In the method by the dry etching, an active layer may be damaged by the etching of the p-type layer, thereby reducing the light emitting characteristic.
Therefore, at the present time, a method by annealing process is devised as shown in FIGS. 3a and 3b.
A semiconductor light emitting device of FIG. 3a has a layer structure comprising a III-V nitride semiconductor on a substrate 21, which comprises an n-type buffer layer 22, n-type GaN clad layer 23, n-type AlGaN clad layer 24, InGaN active layer 25, p-type clad layer 26, and p-type GaN contact layer 27.
In the method, the entire semiconductor layer is annealing-processed, thereby activating the p-type layers. Thereafter, a mask 28 of insulation material is mounted on the surface of the p-type contact layer 27, and the semiconductor is annealing-processed in an ambient of hydrogen. As a result, p-type layers 29 not covered by the mask 28 are made high resistance to form a narrow electric current path as shown in FIG. 3a.
Next, the mask 28 is removed and a p-electrode 30 of Au is mounted on a current injection area of the p-type contact layer 27 as shown in FIG. 3b.
On the other hand, the n-type clad layer 23 is exposed by etching a part of the semiconductor layer (FIG. 3a), and an n-electrode 31 of Au is mounted on the surface of the n-type clad layer 23, thereby forming a semiconductor light emitting device (FIG. 3b).
However, in the method, the mask 28 of insulation material must be removed, and the removed portion is exposed in the atmosphere. The exposed portion is oxidized to form an oxidation film on the portion. Furthermore, in order to reduce the contact resistance of the electrode 31, the semiconductor layer is annealing-processed again. As a result, hydrogen diffuses from the high resistance portion to the low resistance portion of the narrow path, thereby increasing the resistance of the narrow path.